1. Field of the Invention
The present invention relates to a substrate for a liquid crystal display and a liquid crystal display utilizing the same and, more particularly, to a substrate for a liquid crystal display in which color filters are formed on an array substrate having switching elements such as thin film transistors formed thereon and a liquid crystal display utilizing such a substrate for a liquid crystal display.
2. Description of the Related Art
Active matrix liquid crystal displays (LCDs) utilizing thin film transistors (TFTS) as switching elements that have been proposed in the past include inverted staggered structure TFT-LCDs (for example, see Japanese Patent Laid-Open No. JP-A-6-202153). In order to achieve greater aperture ratios, proposals have recently been made on LCDs utilizing an LCD substrate having a CF-on-TFT structure in which color filters are formed on an array substrate having switching elements such as TFTs formed thereon (for example, see Japanese Patent Laid-Open No. JP-A-10-39292). On such an LCD substrate having the CF-on-TFT structure, a passivation film made of an inorganic insulating material is normally formed on TFTs except regions for contact with pixel electrodes.
FIG. 13 is a plan view of an example of one pixel region of an LCD substrate having the CF-on-TFT structure according to the related art, and FIG. 14 is a sectional view along the line B—B in FIG. 13. Gate bus lines (GB) 102 are formed on a transparent insulated substrate 101 that constitutes a TFT substrate 100. An insulation film 103 is formed throughout the substrate over the gate bus lines 102, and drain bus lines (DB) 104 are formed across the gate bus lines 102 with the insulation film 103 interposed therebetween. Regions defined by the gate bus lines 102 and the drain bus lines 104 constitute pixel regions. TFTs 105 are formed in the vicinity of positions where the gate bus lines 102 and the drain bus lines 104 intersect.
A TFT 105 has a drain electrode 108 constituted by a top metal layer 106a and an ohmic contact layer 107a, and it is formed such that an end thereof is positioned on an end of a channel protection film 109 formed above a gate bus line 102. A source electrode 110 constituted by a top metal layer 106b and an ohmic contact layer 107b is formed similarly to the drain electrode 108 at another end of the channel protection film 109. An active semiconductor layer 111 is formed between the insulation film 103 and the channel protection film 109, and the active semiconductor layer 111 is connected to the ohmic contact layers 107a and 107b. In a TFT 105 having such a configuration, the region of the gate bus line 102 directly below the channel protection film 109 serves as a gate electrode, and the insulation film 103 located between those regions serves as a gate insulation film.
A passivation film 112 made of a silicon nitride (Si3NX; hereinafter referred to as “SiN”) is formed above the TFTs 105, and resin CF layers 113 are formed in the pixel regions with the passivation film 112 interposed. An overcoat (OC) layer 114 is formed on the resin CF layers 113, and a transparent oxide electrode film on the OC layer 114 is patterned to form pixel electrodes 115. The pixel electrodes 115 are connected to the source electrodes 110 through contact holes 116a which extend through the OC layer 114 and the passivation film 112. Similarly, the pixel electrodes 115 are connected through contact holes 116b to storage capacitor electrodes 118 that are formed on storage capacitor bus lines (CB) 117 with the insulation film 103 interposed therebetween.
As thus described, the passivation film 112 is formed between the TFTs 105 and the resin CF layers 113 on the TFT substrate having the CF-on-TFT structure according to the related art. For example, resins including pigments dispersed therein as color components are used as the resin CF layers 113, and the passivation film 112 is therefore formed to prevent inorganic components of the pigments from spreading into the active semiconductor layers 111.
However, when the resin CF layers are formed on the TFTs with the SiN passivation film interposed therebetween, the adhesion between the passivation film and the resin CF layers is reduced by changes in the state of a hydroxyl group (OH group) on the surface of SiN with time. This has resulted in problems in that the color filters can come off the SiN surface when the resin CF layers are formed and in that residues of the resin CF layers after etching can remain in contact holes that extend up to the TFTs when the contact holes are formed. Such residues or flakes of color filters can cause problems such as low color purity, and a resultant defect in the patterning of an electrode material formed in a contact hole can result in problems such as lack of contact between the pixel electrode and the TFT.
Incidentally, the documents of the related art are as follows:    [Patent Document 1]    JA-A-6-202153    [Patent Document 2]    JA-A-10-39292